The present invention relates to a method for trueing and dressing grinding wheels and to a novel trueing and dressing tool. More particularly, the present invention relates to a method for trueing and dressing grinding wheels having vitrified-bonded cubic boron nitride (CBN) abrasive by use of a fine point trueing disc mounted between the existing headstock and tailstock of a grinding machine.
A number of grinding wheels are known to those skilled in the art including, for example, conventional aluminum oxide and silicon carbide grinding wheels as well as resin-bonded and vitrified-bonded CBN grinding wheels and diamond grinding wheels. Regardless of the type of grinding wheel, it is necessary to true and dress the grinding wheel in order that it may accurately form fine finishes or precise contours on workpieces.
A variety of methods for trueing and dressing grinding wheels are known in the art, however each has various drawbacks and disadvantages, particularly with regard to trueing and dressing grinding wheels whose abrasive material is vitreous-bonded CBN. One prior art method is disclosed in U.S. Pat. No. 2,791,211 to Nagy and involves periodically indexing a diamond tipped dressing tool in relation to the grinding wheel so that in all indexing positions the diamond is in contact with the wheel in a direction of hard grain forming an angle of between 30.degree. and 45.degree. to a crystal axis of the diamond. While such a single point tool is useful for dressing small diameter grinding wheels, the diamond tip would wear much too rapidly to be useful in dressing large diameter grinding wheels, especially vitrified-bonded CBN grinding wheels.
Alternatives to single point trueing and dressing tools include hand set diamond and metal-bonded diamond rotary cup and straight wheel tools. While such rotary dressing tools are more effective than single point tools, they have the disadvantage of being relatively expensive, and, furthermore, they are used in conjunction with a relatively expensive electric or hydraulic precision drive motor and spindle assembly. Consequently, small machine shops are unable to avail themselves of rotary dressing technology. Another disadvantage of rotary cup wheel dressing tools is the necessity of changing the position or angle of the dressing wheel in order to present new, sharper edges as the originally presented edges wear flat. Straight wheel dressing tools suffer from the further disadvantage of having the abrasive applied to the circumferential surface of the wheel in a band several millimeters in width. As a result, the operator has very little control over the dressed surface of the vitrified-bonded CBN grinding wheels because a wide band of abrasive, unlike a sharp point, generally leaves the wheel in a closed or dull condition. Wheels in this condition generate excessive heat, which may cause the wheel to burn the workpiece.
While such prior art methods are generally considered to be acceptable, manufacturers are always concerned with improving the trueing and dressing process, such as by reducing the time required to true and dress a grinding wheel and reducing the cost of the trueing and dressing tool.